1. Field of the Invention
The present invention relates to a method of forming damascene structures, and more particularly, to a method of forming damascene structures using two anti-reflective coating (ARC) films.
2. Description of the Prior Art
Damascene structure refers to the practice of forming inter-connecting wires first developed by the ancient artisans of Damascus. Damascene structure, including single damascene structure and dual damascene structure, is essential nowadays in the fabrication of inter-connecting wires in semiconductor devices, especially in the fabrication of copper inter-connecting wires. For implementing a single damascene structure, a photoresist pattern is first formed onto a dielectric layer positioned on a substrate to define the positions of the via holes to be etched. Subsequently, an etching process is performed to etch the dielectric layer not covered by the photoresist pattern so as to form a plurality via holes. Finally, the photoresist pattern is stripped, a metal layer is then deposited to fill up the via holes, and a polishing process is performed to form a plurality of inter-connecting wires. As device integration improves day by day, the pattern of the via holes becomes denser and each via hole has an increasingly high aspect ratio. Accordingly, the photoresist pattern used to define the via holes becomes more sophisticated, and therefore has a poor adhesion to the dielectric layer. This makes the photoresist pattern collapse easily during the etching process.
Please refer to FIG. 1 and FIG. 2, which are schematic diagrams illustrating a conventional method of forming a single damascene structure. As shown in FIG. 1, a substrate 10 having a dielectric layer 12 thereon is provided. An anti-reflective (ARC) film 14 is then formed over the dielectric layer 12. Subsequently, a photoresist layer (not shown) is then coated onto the ARC film 14, and an exposure-and-development process is performed to form a photoresist pattern 16 to define the pattern of via holes to be etched later. The ARC film 14 is disposed between the photoresist layer (not shown) and the dielectric layer 12 for the following reason. Over the course of the exposure, the ARC film 14 is able to absorb light beams incident toward the dielectric layer 12 and reduce reflected light beams so that the photoresist pattern 16 developed later is sharp.
As shown in FIG. 2, an etching process is then performed using the photoresist pattern 16 as a mask to etch the region of the dielectric layer 12 unprotected by the photoresist pattern 16 so as to form a plurality of via holes 18. As mentioned earlier, as the pattern of the via holes 18 becomes denser, the photoresist pattern 16 can easily collapse during the etching process as shown in the right portion of FIG. 2, especially on the edge of the substrate 10. Therefore, the prior art suffers from collapse of the photoresist pattern 16, which makes it difficult to form the via holes 18 correctly.